L02: Java Fundamentals and Console Input

Question 1

What does each of these comments represent: //, /*….. /, /**……/?

Answer 1

Single line comment, multi-line comment, Javadoc comment.

Question 2

What are the 3 restrictions to identifiers?

Answer 2

Can’t begin with a digit, can’t be a reserved word, limit length?

Question 3

What are the allowed identifiers?

Answer 3

Letters, numbers, underscore (_), $.

Question 4

What are the guidelines for class names, constants, and variables/methods?

Answer 4

Class Names; MyClass, Car
Constants: MAXIMUM, NUM_OF_WHEELS
Variables, methods: aVariable, fordCar, car_mercedes

Question 5

Is “Class” a valid identifier?

Answer 5

Yes. The reserved word is “class” not “Class”

Question 6

is “1AbC” a valid identifier?

Answer 6

No. Starts with a digit

Question 7

What are the 4 primitive types to represent int in order of size?

Answer 7

byte, short, int, long.

Question 8

What are the 2 ways to represent floating point numbers in order of size?

Answer 8

float, double.

Question 9

What is a char and what is one unique property related to casting?

Answer 9

Stores a single character, and has a unique unicode value. This is why char can be cast to int.

Question 10

What modifier does a constant variable use? What happens if this variable is modified?

Answer 10

final. Throws a compile-error since final variable cannot be modified.

Question 11

What are variables?

Answer 11

Store information, creates a location in memory, must be declared before it is used (ex. int total;) If variable has no value, default value is used.

Question 12

How are Java Class libraries organized?

Answer 12

They are organized into packages. (ex.java.text).

Question 13

How do you import a class (list 2 ways)?

Answer 13

import java.text.DecimalFormat (import the class only)

import java.text.* (imports the entire class)

Question 14

What are the 2 necessary steps to use a scanner?

Answer 14

import java.util.Scanner; // import class
Scanner input = new Scanner(); // Create object

Question 15

When you are done reading inputs, what should be done?

Answer 15

Close the scanner using scanner.close()

Question 16

System.out.println(“x+y=” + x + y);
System.out.println(“x+y=” + (x + y));
If x = 1 and, y = 2, what are the outputs?

Answer 16

x+y=12
x+y=3

Question 17

System.out.println(“this is a
long string”);
Is this a valid way to print a String?

Answer 17

No, you must concatenate.

Question 18

\b, \t, \n, ", ', \. What are these called and what do they do?

Answer 18

Escape sequences to insert special characters into a String. backspace, tab, newline, double quotes, single quotes, backslash.

Question 19

What do these operations evaluate to? 10/8, 8/12, 10.0/8, 8/12.0

Answer 19

1, 0, 1.25, 0.6667

Question 20

What are unary operators?

Answer 20

Operators that act on a single variable (ex. rate++)

Question 21

What are binary operators?

Answer 21

Operators that act on two variables. (ex. rate + bonus)

Question 22

How is this expression evaluated: answer = sum / 4 + MAX * lowest;

Answer 22

/ * + then finally =

Question 23

Explain the difference between post-increment and pre-increment.

Answer 23

Post-increment increments by 1 but uses the old value in the expression. Pre-increment increments by 1 but the new value is used in the expression.

Question 24

int intVariable = 2.99;
double doubleVariable = 2;
Are these expressions invalid or valid?

Answer 24

int is invalid, double is valid

Question 25

What is arithmetic promotion?

Answer 25

If operands are of different types, they are promoted. (short, byte, char) -> int

Question 26

What is the value and type of 2 / 4 * 1.0?

Answer 26

double 0.0. 2/4 is evaluated first as 0 then multiplied by double so arithmetic promotion.

Question 27

What is the value and type of 1.0 * 2 / 4?

Answer 27

1.0 * 2 evaluated first as 2.0 then / 4 evaluates to 0.5.

Question 28

What is assignment conversion?

Answer 28

If a variable has wider type than expression then the expression is widened automatically. If a variable has a smaller type than the expression then there will be a compilation error.

Question 29

What is casting?

Answer 29

Explicitly forcing a type conversion.

Question 30

double d;
d = 2/4;
d = (double) 2/4;
d = (double)(2/4);

Answer 30

d = 0, d = 0.5, d = 0.0

Question 31

String name = “Your Name Here”
a. name.substring(9) ;
b. name.substring(1,6);
c. name.substring(1,name.length()-1);
d. name.length();
e. name.indexOf(‘r’);
f. name.indexOf(‘n’);

Answer 31

a. “ Here”
b. “our N”
c. “ our Name Her’
d. 14
e. 3
f. -1